init is the program which is used on most Linuxes to generate all other processes on bootup.
The BSD style (which runs from the /etc/rc script) is slightly different from the SysV style: SySV is probably the one you're familiar with, as it's used by Debian, SuSE, and until recently, Redhat. With this setup, the system checks /etc/inittab to find a default runlevel. This file also defines what to do for various runlevels. A runlevel is a way of specifying a particular set of processes to run.
http://www.linuxlinks.com/portal/news/article.php?story=20090505141043712